Amplifiers are ubiquitous components in experimental physics, and are typically used to raise the energy of a signal coming from a measurement device to a level sufficient to exceed the noise of the electronics used to read the signal. Conventional amplifiers are dissipative and generally generate a certain amount of noise in addition to an amplified output signal in response to an input signal applied to an input terminal.
Quantum information processing uses quantum mechanical phenomena, such as energy quantization, superposition, and/or entanglement, to encode and process information in a way not utilized by conventional information processing. It is expected that certain computational problems may be solved more efficiently using quantum computation rather than conventional classical computation. Due to the low energies used in a quantum circuit, measurements of a quantum circuit require amplification before they can be read at a macroscopic (non-quantum) scale. Conventional amplifiers are, however, unsuitable for use in quantum circuits as they introduce too much noise to produce a useable output signal and exhibit poor sensitivity to the low energies of a quantum circuit.